This invention relates to thermoplastic composite films. More particularly, this invention relates to a multilayer thermoplastic composite adhesive film which is particularly useful in automotive interior trim applications, for example, in headliner applications.
The construction of most automotive interior headliners requires an adhesive material to bond headliner components together, e.g., a facing material, such as a polyurethane foam-backed fabric, to a molded headliner insulation shell material such as fiberglass. A typical headliner composite includes a molded, structural shell, an adhesive, a polyurethane foam and a cover material/fabric.
The shell materials include fiberglass, fiberglass reinforced urethane foam, resinated nonwoven materials, polyester fiber composites, paperboard and combinations of paperboard and polyethylene foam or styrene-maleic anhydride (SMA) foam. With most structures, the base substrate is formed in matched metal tool molding operations and trimmed to the specific dimensions. The cover materials typically are constructed of either polyether or polyester urethane foam flame laminated to nylon fabric. Some structures include woven fabrics, needle-punched textiles or thermoplastic elastomer covers without foam backings.
Heretofore, a variety of adhesive systems have been used to carry out the process of permanently bonding the facing material to the molded headliner shell including wet adhesives, both solvent and water-borne, dry powdered adhesives, hot melt adhesives, mechanical fasteners and solid adhesive polymer films.
Wet adhesive systems are typically applied directly on the molded shell by manual or automated spray equipment. The adhesive coated shells are then processed through drying ovens to volatilize the carrier solvent. The cover material is bonded to the shell in a secondary molding operation.
Adhesive films are commonly applied by two processes. First, the adhesive film may be applied by an in-mold technique where the film is placed on a base substrate in the molding process with the cover material. The process may be simplified by mounting a film roll on an unwind stand at the rear of the molding process and unwinding the adhesive film and the cover material in unison.
Second, the adhesive film can be pre-applied to a foam backed fabric via a hot roll or flame lamination process. Adhesive films which are heat activated, thermoplastic adhesive polymers can be bonded to the cover material and reactivated to bond to the base substrate during the molding operation. As a result, the adhesive laminated facing can be placed directly on a base shell in the molding process, eliminating the process of handling the free film. Adhesion values in the range of 0.75 to 1.00 lbs./inch width (3.3 to 4.4N/2.54 centimeters width) are typically achieved during the flame lamination process with polyether and polyester urethane foams and result in a cohesive failure of the foam cells.
A thin gauge (1 to 6 mils (25.4 to 152 microns)) ethylene acrylic acid blown monolayer adhesive film such as Dow Adhesive Film (DAF) 899A commercially available from The Dow Chemical Company, have heretofore been commercially used as a headliner adhesive film for bonding rigid fiberglass shells to polyurethane foam backed fabric. Adhesive selection has typically been based on performance, system economics, and the ability to be processed on existing equipment. The introduction of new base shell materials, designs, regulatory issues, processes and application requirements have placed new demands on the adhesive system. Ideally, the adhesive system must bond to a variety of substrates and cover materials, conform and adhere to molded contours and perform consistently on various processes with improved productivity and quality without creating additional waste disposal or environmental concerns.
Recent development efforts have been focused on designing new adhesive polymer film systems to satisfy the emerging application needs of the interior headliners.
It is therefore desired to provide a new adhesive film for interior headliners fabrication which meets both process and performance requirements while complying with all current headliner specifications.
It is also desired to provide an adhesive film that has the advantages of a non-tack surface for easier handling and the ability to reactivate the adhesive nature of the film by a subsequent heating process.
Some key adhesive film properties desired based on Automotive Original Equipment Manufacturer (OEM) specifications for bonded interior trim, adhesives and adhesive films are initial bond strength (substrate failure) and bond strength after climate simulation testing such as humidity and heat exposure (no loss of properties). A critical application test is the softening point test which measures bond strength under load at elevated temperatures. Another key adhesive need identified in the headliner fabrication process from a manufacturing perspective, includes the ease of handling. To address this need requires designing an adhesive which can be pre-laminated to the cover material to eliminate adhesive handling. Also, the adhesive film must not cause wrinkles in the facing during molding by significantly increasing the stiffness of the cover material. In addition, an adhesive film is required with closed mold cycles of less than 20 seconds to ensure fabrication efficiency. Furthermore, the adhesive film must not create additional waste disposal or environmental concerns. Thus, the film design is limited to materials which do not contain any regulated components.
The industry tends toward new materials and additional contoured shapes require the adhesive to perform on a variety of substrates and molded designs. As a result, there is a need for an adhesive film designed to bond to polyether and polyester urethane foam, unbacked fabrics, and various base headliner substrates. Also, there is a need for a product substrate which is formulated to stretch, conform and adhere on deeply contoured headliners.